The primary goal of the proposed research is to determine how the diencephalic and telencephalic auditory centers of anurans respond to complex species-specific sounds. Neurophysiological recordings will be conducted on a species (Hyla gratiosa) whose vocal signals have certain spectral characteristics and whose behavioral preference for synthetic calls have been studied previously. Recordings will be made from both immobilized and awake-behaving animals with chronically implanted electrodes so that the effects of the environment and the behavioral state of the animal on the response characteristics of the higher auditory areas can be determined. The single unit studies of these centers will resolve if a limited hierarchical processing system exists in the central auditory pathway of anurans. The research is important since it will lead to an understanding of how complex sounds are analyzed and detected by the brain of a relatively simple vertebrate. In addition the research will add to our understanding of the processing of acoustic information in animals with more complex vocal repertoires including the processing of speech in humans.